Liquid crystal display devices are more advantageous than CRT (Cathode Ray Tube) display devices in that the liquid crystal display devices (i) are thinner and lighter, (ii) can be driven at a low voltage, and (iii) require less power consumption. This advantage causes the liquid crystal display devices to be used in various electronic devices such as a TV, a notebook PC (personal computers), a desktop PC, a PDA (Personal Digital Assistant), and a mobile phone.
The liquid crystal display devices are driven in a mode such as a TN mode (Twisted Nematic Mode), an STN mode (Super Twisted mode), or a VA mode (Vertically Aligned Mode). In the TN mode and the STN mode, liquid crystal molecules are horizontally aligned. In the VA mode, liquid crystal molecules are vertically aligned. The VA mode out of modes has been widely used in recent years because of its high contrast and its excellent viewing angle characteristic.
In a case of driving a liquid crystal display device in the VA mode, liquid crystal with negative dielectric anisotropy is used to form vertical alignment films on respective two electrodes that face each other. The vertical alignment film causes liquid crystal molecules to be vertically aligned. With the configuration, it is possible to achieve a desired display, by applying a voltage to the liquid crystal molecules, which are vertically aligned between the two electrodes, so that the liquid crystal molecules are tilted in predetermined directions.
Note that the VA mode is a type of a so-called birefringence mode. In the birefringence mode, transmittance is determined in accordance with a phase difference occurring while light is being transmitted through a liquid crystal panel. That is, the transmittance is determined on the basis of refractive index anisotropy (Δn) of liquid crystal, a thickness (d) of a liquid crystal layer and a wavelength (λ) of the light. On this account, even if an identical voltage is applied to liquid crystal panels having an identical structure, their voltage-transmittance characteristics (V-T characteristic) vary depending on the wavelengths of the light. The liquid crystal display devices are generally configured by respective pixels R (red), G (green), and B (blue) so as to carry out color display. In the VA mode, transmittance (i.e., light transmittance) varies from color to color, so that tinge varies delicately with a gray scale. Further, each maximum transmittance of a corresponding one of the colors R, G, and B (Tmax (R), Tmax (G), and Tmax (B)) occurs and differs when a corresponding voltage is applied.
FIG. 10 is a graph showing a relation between transmittance and retardation Δn×d (hereinafter, merely referred to as ‘Δnd’) of liquid crystal at each wavelength in a liquid crystal panel of the VA mode. FIG. 10 shows a change in transmittance with respect to a change in Δnd at each wavelength (R: 670 nm, G: 550 nm, and B: 450 nm).
As indicated in FIG. 10, if a thickness of the liquid crystal layer is set to Δnd at which luminance becomes a maximum value during white display in the VA mode (i.e., Δnd at which transmittance of light with a wavelength of 550 nm becomes a maximum value), then transmittance of light with a wavelength of 450 nm becomes too low. In view of the circumstances, a thickness of a liquid crystal layer has been conventionally set to be smaller than the thickness determined on the basis of the maximum luminance so that color is prevented from appearing in the white display.
On this account, the luminance is darker during the white display in the VA mode than in the TN mode. As such, it is necessary to increase backlight luminance so as to obtain white luminance which is substantially identical to that of a liquid crystal panel of the TN mode.
Note, however, that increasing the backlight luminance requires increasing power consumption of an illumination device. This causes a smaller range of applicability of the liquid crystal panel. In a case where the thickness of the liquid crystal layer is set larger for the sake of white luminance, the transmittance of the light with a wavelength of 450 nm becomes excessively lower than that in the TN mode. This causes a problem that the panel gets yellowish during the white display.
A so-called multi gap structure is known as a technique for addressing such a problem. In the multi gap structure, thicknesses of respective liquid crystal layers are separately set for respective pixels R, G, and B so that the pixels have their respective maximum transmittances in response to an applied driving voltage. Namely, in a liquid crystal display device having the multi gap structure, the thicknesses of the respective liquid crystal layers are separately set for the respective pixels R, G, and B so that the pixels R, G, and B have their respective maximum transmittances when an identical voltage is applied to the pixels R, G, and B. Therefore, in a case where the multi gap structure is applied to a vertical alignment liquid crystal panel in which the display is carried out in the VA mode, it is possible to avoid getting colored during the white display and to attain transmittance which is substantially identical to that of the TN mode.